RE: [PHP] Speaking of OOP

[Neil Kimber]

Two of the greatest benefits of OO design is polymorphism.

Polymorphism allows you to build complex systems in a simple manner. A
simple example that is easy to visualise would be considering a system that
draws different objects to a screen. Each object could be a vector image
(i.e. a list of points to connect lines) or a jpg binary image. You could
create a different class to handle each class of drawing object. You could
then give each class the same draw() method, although the implementation
would be different in class. Now, here's were polymorphism kicks in, you can
write some code that keeps a list of graphics objects to draw and loop
through that list simply calling

myDrawingObject[numIndex]->draw();

At no stage does your controlling code need to understand the difference
between the different base classes. Your controlling code will happily draw
any graphic object. Indeed, you could now add new base drawing classes and
your controlling code would handle these equally well with no need for code
changes.

This is a wondefully powerful concept.

p.s. inheritance is pretty cool too.



-----Original Message-----
From: Ignacio Vazquez-Abrams [mailto:[EMAIL PROTECTED]]
Sent: 09 January 2001 22:35
To: John Guynn
Cc: Php (E-mail)
Subject: Re: [PHP] Speaking of OOP


On Tue, 9 Jan 2001, John Guynn wrote:

> I am a hardware guy hacking my way through building dynamic web pages
using
> PHP and MySQL and I just can't get the concept of OOP.  I don't understand
> what a class can offer that I can't do with a function.  I've tried to
read
> a couple of books about OOP and a chapter about classes and such in a PHP
> book and I just can't grasp the concept.
>
> Can someone explain to me how a class makes my life easier compared to
using
> functions.
>
> Thanks in advance,
>
> John Guynn
>
> This email brought to you by RFCs 821 and 1225.
>

You are absolutely right. There is not one single thing that can be done
with
classes that couldn't be done with functions. Not in PHP anyway. The main
use
of OOP is the abstraction of data along with the code used to manipulate it.
Observe:

<?php
$circle=Array();
$circle["radius"]=5;

$square=Array();
$square["width"]=4;
$square["length"]=3;

function area1($w, $h)
{
  return $w*$h;
};

function area2($shape)
{
  return $shape["width"]*$shape["height"];
};

$squarearea=area1($square["width"], $square["height"]);
$badarea=area1($square["height"], $circle["radius"]);

$squarearea=area2($square);
$badarea=area2($circle);
?>

Now using OOP:

<?php
class Circle
{
  var $radius;

  function Circle($r=0)
  {
    $this->redius=$r;
  }

  function area()
  {
    return $this->radius*$this->radius*3.1415;
  }
};

class Square
{
  var $width;
  var $height;

  function Square($w=0, $h=0)
  {
    $this->width=$w;
    $this->height=$h;
  }

  function area()
  {
    return $this->width*$this->height;
  }
};

$circle=New Circle(5);
$square=New Square(4, 3);

$circlearea=$circle->area();
$squarearea=$square->area();
?>

In short, OOP makes it just slightly more difficult to screw things up.
PHP's
OOP model is missing two things (field scope [private, protected, public]
and
class destructors) that prevent it from being as powerful as it could
be, but
it beats flipping switches :)

--
Ignacio Vazquez-Abrams  <[EMAIL PROTECTED]>







--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
To contact the list administrators, e-mail: [EMAIL PROTECTED]



-- 
PHP General Mailing List (http://www.php.net/)
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
To contact the list administrators, e-mail: [EMAIL PROTECTED]